Process and apparatus for continuously producing an elatomeric composition

ABSTRACT

A process for continuously producing an elastomeric composition includes metering and feeding at least one elastomer and at least one filler into at least one extruder, mixing and dispersing the at least one filler into the at least one elastomer using the at least one extruder, and passing the composition that results through at least one static mixer. An apparatus for continuously producing the composition includes at least one twin-screw extruder, at least one metering device, and at least one static mixer. The at least one extruder includes a housing and two screws rotatably mounted in the housing. The housing includes at least one feed opening and a discharge opening. The at least one metering device meters and feeds at least one elastomer and at least one filler into the at least one extruder. The composition discharged from the discharge opening passes through the at least one static mixer.

The present invention relates to a process and an apparatus forcontinuously producing an elastomeric composition. More particularly,the present invention relates to a process and apparatus forcontinuously producing an elastomeric composition by means of at leastone extruder, the resulting elastomeric composition being primarily, butnot exclusively, intended for use in the production of tyres.

Conventionally, the production of elastomeric compositions (in thefollowing also indicated as “rubber mixtures”) is performed batchwise bymeans of internal mixers, usually Banbury mixers having twocounter-rotating rotors which exert an intensive mixing action tomasticate the rubber ingredients and to incorporate and thoroughlydisperse therein the other ingredients such as fillers, lubricatingaids, curatives and auxiliary substances.

The compounding process using internal mixers shows many drawbacks,particularly a poor heat dissipation and thus a scarce temperaturecontrol, mainly due to an unfavourable ratio between material volume andmixer surface area. To improve dispersion in the rubber base, thevarious ingredients, and particularly the fillers, are incorporated intothe rubber base in batches distributed in a plurality of mixingoperations separated by cooling and stocking steps. Temperaturesensitive ingredients, such as cross-linking agents and accelerators,are added only during the final mixing step after cooling the rubbermixture below a predetermined temperature (usually below 110° C.) toavoid scorching.

Therefore, the compounding process in internal mixers, although stillremaining the most widelv used mixing process in the rubber industry, istime and energy consuming and does not guarantee an effective control onthe characteristics of the resulting elastomeric compositions,particularly as regards dispersion homogeneity of fillers into therubber base. Variation in the added amounts of individual ingredients,timing of addition and discharge from the mixers, initial temperature ofthe raw materials, and fluctuations of shear forces inside the materialduring mixing, all contribute to batch-to-batch variation.

To overcome the limitations of the discontinuous processes, manyattempts have been performed by the rubber industry to set up continuouscompounding processes, based on extrusion techniques analogous to thosecommonly employed in the processing of thermoplastic polymer materials.Continuous mixing processes carried out by means of an extruder shouldimprove uniformity in the rubber mixture characteristics, better thermalmanagement resulting from improved surface-to-mass ratios, and possibledevelopment of highly automated operations. For an overview on thissubject see the article “A tale of continuous development” by H.Ellwood, published in European Rubber Journal, March 1987, pages 26-28.

U.S. Pat. No. 4,897,236 discloses a process and an apparatus forcontinuously producing a rubber mixture, wherein the ingredients of themixture are fed, masticated and homogenized in a twin-screw extruder.The resulting mixture is divided into a first and a second portion. Thefirst portion is discharged, while the second portion is recycled forfurther homogenization and for mixing with fresh batches of theingredients being fed into the extruder. The recycled portion iscirculated to and returned from a cooled, annular chamber exterior tothe extruder chamber, said annular chamber having outflow and inflowpassages communicating with the interior of the extruder. That partialrecycling of the rubber mixture should compensate for fluctuations inthe metering of the ingredients and for local inhomogeneities which mayoccur. Moreover, the intensive cooling of the recycled portion in theannular chamber should correct a rising processing temperature, andshould improve the dispersing action because of increased shearingstresses consequent to the temperature decrease.

U.S. Pat. No. 5,302,635 discloses a method and apparatus forcontinuously producing a rubber composition. In a first step, cruderubber is continuously fed into a twin-screw extruder, added withnon-reactive additives (oils and fillers) and the resulting mixture isplasticated and homogenized by the extruder screws. During that firststep, the mixture is kept at a temperature of from 100° C. to 160° C.Then, in a second step, the resulting mixture is cooled to a temperatureof from 100° C. to 120° C. and reactive additives (particularly sulfurand vulcanization accelerators) are fed and incorporated into the rubbermixture. The homogenized rubber composition then leaves the extruder viathe extruder outlet opening.

The process can be carried out according to different extruderconfigurations. For instance, the two mixing steps can be performed in asingle twin-screw extruder having two distinct mixing zones operating attwo different temperatures. Alternatively, the first step may be carriedout in a first twin-screw extruder operating at 100° C.-160° C.; theresulting base composition is then fed directly to a second twin-screwextruder operating at 100° C.-120° C. According to another embodiment,the process may be performed in a single extruder having two screw pairsdriven at mutually opposite ends of the extruder housing, the two screwpairs operating at different temperatures.

U.S. Pat. No. 5,158,725 discloses a method for continuously producingelastomer compositions which comprises: feeding an elastomer into atwin-screw extruder; feeding at least one filler, oil and/or otherelastomers into the extruder; mixing the ingredients to provide ahomogeneous mixture which is maintained at a Mooney viscosity ML(1+4) at100° C. between 20 and 250 during mixing; discharging the resultingmixture from the extruder. Precise volumetric or loss-in-weight feedersare used to meter the elastomer and other ingredients into the extruder.After leaving the extruder, the compounded rubber may be extrudedthrough a die, calendered into sheets, strips or strands, or may bepelletized. The continuous method is less expensive than the multi-stepbatchwise processes currently used in the art and requires less manpowerand less material handling. Moreover, improved dispersion andhomogeneity of the resulting elastomeric compositions would result.

U.S. Pat. No. 5,262,111 discloses a process for the continuousproduction of a rubber composition in a twin- screw extruder. Rubber isfed into the extruder together with a processing aid and masticated upto a temperature of 120° C. to 180° C. Subsequently, a first part ofcarbon black, representing preferably 40-80% of the whole quantity ofcarbon black, is fed into the heated extrudate. Afterwards, plasticizingoil is added to the extrudate before the second remaining carbon blackpart is fed and incorporated into the extrudate at a temperature of from120° C. to 180° C. The whole composition is then cooled to a temperatureof from 100° C. to 120° C., a crosslinking agent is added, and thecomposition is homogenized and extruded. The process would improve thedispersion of carbon black in the extrudate while reducing the specificenergy requirement.

U.S. Pat. No. 5,626,420 discloses a continuous mixing process andapparatus, wherein base elastomer(s) and other components arecontinuously dosed and introduced into a mixing chamber formed of astator and a rotor rotating therein, preferably a single screw extruder.The introduced components advance within the mixing chamber along zonesof propulsion and mixing. To improve dispersion and homogenization ofthe rubber components, the filling rate of the mixing chamber in atleast certain mixing zones is lower than 1. To properly introduce thecomponents, and particularly the rubber base, into the mixing chamber,force feeding means are used, such as volumetric pumps (e.g. gearpumps). To obtain precise dosage of the different components, it may bedesirable to add the components in a mixing zone where the filling rateis equal to 1, located between two mixing zones having a filling ratelower than 1.

U.S. Pat. No. 5,374,387 describes a process for continuously producingelastomeric compositions using a twin-screw extruder, which comprisesthe following sequential steps. In a first mixing zone of the extruderan elastomeric material is added, sheared and heated to a firstoperating temperature (typically from 130° C. to 220° C.) while reducingviscosity. Then the elastomeric material is passed in a second mixingzone where it is added with at least a first portion of a reinforcingfiller and processing aid, while simultaneously cooling the rubbermixture to a second operating temperature (typically from 110° C. to160° C.). The resulting mixture is then passed to an optional thirdmixing zone, where small constituent chemicals, such as adhesionpromoters, anti-ozonants, color additives, fire retardants and the like,are introduced into the rubber mixture. Preferably, in said third mixingzone a second portion of the reinforcing filler and processing aid isadded so as to reach a third operating temperature (typically from 85°C. to 130° C.). Then, in a fourth mixing zone the rubber mixture issupplemented with the vulcanization agent at a fourth operatingtemperature (typically from 115° C. to 150° C.). The mixture flow isthen directed through a delivery zone (fifth zone) wherein the mixtureflow is extruded into the desired form through some sort of die slot orthe like. The various components of the rubber composition arecontinuously and individually metered to the extruder, preferably in theform of particulated materials and/or liquids by means of weight lossfeeders.

U.S. Pat. No. 5,711,904 discloses a method for continuous mixing ofelastomeric compositions reinforced with silica. A twin-screw extruderis fed with the elastomeric material, then with silica and othercompounding ingredients, including a silica coupler. Temperature andpressure along the extruder are controlled to enable the silica couplerto react with the silica and the elastomeric material. Then curativesand accelerators are added, while maintaining the mixture at a Mooneyviscosity ML(1+4) at 100° C. between 20 and 250. The mixing is continuedfor a time sufficient to thoroughly mix the curatives and accelerators.The resulting elastomeric composition is then forced through a suitabledie mounted at the extruder exit. The overall process may be performedusing a single extruder or a sequence of extruders. Preferably,residence time is increased in a first twin-screw extruder and then thecomposition is cooled, ground and dumped into a second twin-screwextruder where the rubber mix is completed with curatives and otheringredients. The different extruders may be separate independententities or may be coupled to each other to form one continuous process.The extruders may be closely coupled in a cross-head extruder mounting,or may be more loosely connected, for instance via festoons or beltsthat convey the material from one unit to the other.

The Applicant has noted that, in a process for continuously producing anelastomeric composition by means of at least one extruder, the resultingelastomeric composition may not have a uniformity of properties as wouldbe expected taking into account the very good control of the processingconditions achievable during extrusion.

In particular, the Applicant has noted that the mixing performance ofthe extruder is limited by the introduction of the temperature sensitiveminor ingredients which require a very strict control of the temperatureinto the extruder to avoid scorching. Moreover, said temperaturesensitive minor ingredients are generally introduced into the extruder'sbarrel in correspondence of the end zone thereof. Therefore, they arenot sufficiently mixed together and uniformly homogenized with theplurality of ingredients to be compounded.

In particular, the Applicant has noted that the resulting elastomericcomposition exiting from a continuous production process is notsatisfactory in terms of consistency (i.e. of uniformity) of thephysical-chemical properties, said properties varying from sample tosample even within the same production campaign causing a correspondingvariation of performance in the finished product.

The Applicant has noticed that the above considerations are ofparticular relevance when applied to the so called “minor ingredients”,i.e. to those components which are different from rubbers, reinforcingfillers and plasticizing agents and which are added to modify and/or toimprove the characteristics of the elastomeric compositions. Someexamples of said minor ingredients are: crosslinking agents,crosslinking accelerators, crosslinking retardants, crosslinkingactivators, protective agents, hardening resins, adhesion promoters,coupling agents, condensation catalysts.

The addition to the rubber base of the minor ingredients, types andamounts of which vary according to the elastomeric composition to beproduced, is particularly critical since the minor ingredients are veryS numerous (usually at least 5-15 in a single rubber mixture) and usedin little amounts (generally not greater than 5% by weight with respectto the total weight of the rubber mixture). Therefore, a very accuratedistribution and uniform homogenization of said minor ingredients arerather difficult to be achieved.

The Applicant has now found that an excellent uniformity of thephysical-chemical properties of the elastomeric composition exiting fromthe extrusion apparatus can be obtained by providing the productionprocess with a mixing step to be carried out in a static mixer.

Therefore, in a first aspect the present invention relates to a processfor continuously producing an elastomeric composition, said processcomprising the steps of:

-   -   metering and feeding into at least one extruder at least one        elastomer and at least one filler;    -   mixing and dispersing said filler into said elastomer by means        of said extruder, and    -   passing the resulting elastomeric composition through at least        one static mixer.

The Applicant has found that said step passing the resulting elastomericcomposition through a static mixer, wherein a further mixing step iscarried out, advantageously ensure the reproducibility of thephysical-chemical properties of said resulting elastomeric composition.

In accordance with a preferred embodiment, the process of the presentinvention comprises the steps of discharging the resulting elastomericcomposition from said extruder and cooling said composition before thestep of passing the latter through a static mixer.

Preferably, said extruder is a twin-screw extruder.

According to a preferred embodiment, the process of the presentinvention comprises the steps of metering and feeding into said extruderat least one minor ingredient which is mixed and dispersed into saidelastomer by means of said extruder.

Preferably, the minor ingredients metered and fed into said extruder donot include temperature sensitive minor ingredients.

According to a further embodiment, the process of the present inventioncomprises the step of adding at least one minor ingredient to theresulting elastomeric composition discharged from the extruder.

Preferably, said step of adding is carried. out after said step ofcooling.

Preferably, the temperature sensitive minor ingredients are added to theresulting elastomeric composition discharged from the extruder. This isparticularly advantageous since the working conditions of the extruderare not limited by the temperature sensitive minor ingredients. Inparticular, the absence of said temperature sensitive minor ingredientsduring the steps of mixing and dispersing does not limit the maximumtemperature which can be reached within the extruder.

Preferably, the minor ingredients are fed into the extruder or added tothe resulting elastomeric composition discharged from the extruder inthe form of a subdivided product. According to the present invention,the term “subdivided product” refers to a product in discrete particles.Preferably, said particles have average dimensions of from 0.5 mm to 15mm, more preferably from 1 mm to 10 mm, even more preferably from 3 mmto 7 mm. Preferably, said particles are in the form of granules,pellets, beads or pearls.

Alternatively, the minor ingredients are fed into the extruder or addedto the resulting elastomeric composition discharged from the extruder inthe form of a powder.

Alternatively, the minor ingredients are fed into the extruder or addedto the resulting elastomeric composition discharged from the extruder inthe form of a liquid.

Alternatively, the minor ingredients are fed into the extruder or addedto the resulting elastomeric composition discharged from the extruder inthe form of a masterbatch.

Advantageously, said masterbatch can be obtained by mixing anddispersing, preferably into an additional extruder, at least one minoringredient and a predetermined amount of the resulting elastomericcomposition discharged from the extruder.

The masterbatch resulting from said additional extruder can be obtainedin the form of a continuous ribbon or, alternatively, in the form of asubdivided product.

According to a preferred embodiment, the process of the presentinvention further comprises the step of obtaining a subdivided productfrom the resulting elastomeric composition discharged from the extruder.

According to a preferred embodiment, said step of obtaining a subdividedproduct from the resulting elastomeric composition discharged from saidextruder is carried out at the discharge opening of said extruder sothat the extrudate is obtained directly in the subdivided form.

According to a further embodiment, said step of obtaining a subdividedproduct from the resulting elastomeric composition discharged from saidextruder is carried out after said step of cooling.

According to a further embodiment, the process of the present inventionfurther comprises the steps of:

-   -   accumulating an amount of said subdivided product obtained from        the resulting elastomeric composition discharged from said        extruder, and    -   stirring said accumulated amount of subdivided product.

The Applicant has perceived that accumulating and stirring for apredetermined period of time an amount of elastomeric extrudate in theform of a subdivided product, e.g. by means of a rotating drum,compensate for any possible fluctuations in the metering step of thevarious ingredients as well as for any local inhomogeneities which mayoccur during the production process. The Applicant has noted that saidinhomogeneities, i.e. the lack of consistency of the physical-chemicalproperties mentioned above, are mainly due to fluctuations which mayoccur during the metering of the plurality of ingredients which areadded to produce the elastomeric composition. The Applicant has foundthat said accumulating and stirring steps allow to mechanicallyhomogenize subdivided products which are obtained at different momentsof the production process so that any possible fluctuations occurredduring the metering and feeding steps can be advantageously compensated.

According to a preferred embodiment, said steps of accumulating andstirring are carried out after said step of obtaining a subdividedproduct from the resulting elastomeric composition discharged from saidextruder.

According to a further embodiment, the steps of accumulating andstirring are carried out also on the subdivided product obtained from atleast one minor ingredient.

According to a further embodiment, the step of adding at least one minoringredient to the resulting elastomeric composition discharged from theextruder is carried out before said steps of accumulating and stirring.

Alternatively, the step of adding at least one minor ingredient to theresulting elastomeric composition discharged from the extruder iscarried out after said steps of accumulating and stirring.

According to a preferred embodiment of the present invention thedischarging of the stirred subdivided product is carried outcontinuously.

According to a further embodiment, the discharging of the stirredsubdivided product is performed batchwise at the end of the stirringstep by means of at least two stirring devices which are arranged inseries so that while a first one is stirring, a second one is loadedwith or unloaded from the subdivided product.

According to a preferred embodiment, the process of the presentinvention further comprises a discharging step of the elastomericcomposition passed through said static mixer. Preferably, saiddischarging step is carried out continuously. Alternatively, saiddischarging step is carried out batchwise.

According to a preferred embodiment of the present invention, theresulting elastomeric composition is cooled down to prevent scorching.Preferably, the resulting elastomeric composition, discharged from theextruder, is cooled down by air at room temperature contacting saidelastomeric composition during the transfer thereof towards thesuccessive operating unit. Alternatively, said step of cooling iscarried out by using any cooling device known in the art such as, forinstance, a cooled conveyor belt, a cooled air flow directed onto theresulting elastomeric composition, or causing the latter to pass into acooling conduit containing a coolant (typically water) and successivelyto dry by hot air. Preferably, said elastomeric composition is cooleddown at a temperature not higher than 110° C., more preferably at atemperature ranging from 20° C. to 90° C., even more preferably from 25°C. to 80° C.

In a second aspect the present invention relates to an apparatus forcontinuously producing an elastomeric composition, said apparatuscomprising:

-   -   at least one twin-screw extruder comprising a housing and two        screws rotatably mounted in said housing, said housing including        at least one feed opening and a discharge opening;    -   at least one metering device to meter and feed into said        extruder at least one elastomer and at least one filler, and    -   at least one static mixer for passing through the resulting        elastomeric composition discharged from said discharge opening        of said extruder.

According to an embodiment of the present invention, said static mixeris positioned at the discharge opening of said extruder.

According to a further embodiment of the present invention, said staticmixer is positioned downstream of said extruder.

According to a preferred embodiment of the present invention, saidapparatus comprises at least one further metering device to meter andfeed into said extruder at least one minor ingredient. Preferably, theminor ingredients fed into the extruder do not include the temperaturesensitive minor ingredients.

According to a preferred embodiment of the present invention, saidapparatus comprises at least one further metering device to meter add atleast one minor ingredient to the resulting elastomeric compositiondischarged from the discharge opening of the extruder. Preferably, thetemperature sensitive minor ingredients are added to the resultingelastomeric composition discharged from the extruder.

Accordlng to a preferred embodiment of the present invention, saidapparatus comprises at least one cooling device upstream of the staticmixer.

According to a preferred embodiment of the present invention, saidapparatus further comprises at least one device for obtaining asubdivided product from the resulting elastomeric composition dischargedfrom the discharge opening of the extruder. Preferably, said device forobtaining a subdivided product from the resulting elastomericcomposition is positioned at the discharge opening of the extruder sothat the extrudate is obtained directly in the subdivided form.

Alternatively, said device is positioned downstrean of said extruder.Preferably, said device is a granulator or an open mill.

According to a preferred embodiment of the present invention, saidapparatus further comprises at least one stirring device for mixing theaccumulated subdivided product obtained from the resulting elastomericcomposition discharged from the extruder.

Preferably, said stirring device is positioned upstream of the staticmixer. Preferably, said stirring device is a rotating drum.

According to a preferred embodiment of the present invention, saidmetering devices of the apparatus according to the present invention aregravimetric feeders.

According to a preferred embodiment, the elastomeric composition is fedinto at least one static mixer by means of a feeding and pumping device.Said feeding and pumping device provides said composition with thepressure which is necessary for causing it to pass through the staticmixer.

According to an embodiment of the present invention, said feeding andpumping device is positioned upstream of the static mixer. Preferably,said feeding and pumping device is a gear-pump.

According to a further embodiment, said feeding and pumping device ispositioned at a feed opening of said static mixer. Preferably, saidfeeding and pumping device is a gear-pump or a single-screw extruder ora reciprocating screw, or combinations thereof. Particularly preferredis the combination single-screw extruder and gear-pump.

According to a preferred embodiment, the apparatus of the presentinvention further comprises at least one filtering body positionedupstream of the discharge openining of the extruder.

The present invention is now further illustrated with reference to theattached figures wherein:

FIG. 1 is a schematic diagram of a traditional plant for producing anelastomeric composition, and

FIGS. 2 to 10 are schematic diagrams of different embodiments of acontinuous production plant of an elastomeric composition according tothe present invention.

For simplicity of description, in the appended drawings, the samereference signs correspond to similar or identical components.

FIG. 1 shows a schematic diagram of a production plant 100 of anelastomeric composition according to the prior art.

Said production plant 100 comprises an extruder 110 suitable forproducing a continuous ribbon (or rod) E of the desired elastomericcomposition. As schematically shown in FIG. 1, by means of feed hoppers111 the extruder 110 is fed with the recipe ingredients necessary forproducing said desired elastomeric composition, said ingredientstipically comprising: rubber base materials, reinforcing fillers andminor ingredients as defined above.

Generally, the recipe ingredients are fed to different zones of theextruder. For example, FIG. 1 shows three main flows A, B, C incorrespondence of three different zones of the extruder 110, the numberof said flows depending on the elastomeric composition to be produced.

Furthermore, generally some recipe ingredients are fed to the extrudermore than once, for instance the same recipe ingredient can be fed totwo distinct zones of the extruder, once again depending on theelastomeric composition to be produced. Therefore, each flow A, B, C ofFIG. 1 can comprise more than one recipe ingredient. That is the case,for instance, of the reinforcing fillers (e.g., carbon black, silica)which are preferably introduced at different zones of the extruder so asto improve their dispersion in the rubber base.

According to said embodiment, the temperature sensitive minoringredients are introduced into the extruder 110 in correspondence ofthe last feed hopper thereof.

For simplicity, FIG. 1 shows only one metering device 112 for each flowA, B, C. However, in the case each flow comprises more than one recipeingredient, preferably each recipe ingredient is provided with adedicated metering device. In that way, metering errors which can occurdue to the metering of recipe ingredients of different densities can beadvantageously reduced.

Alternatively, a plurality of different recipe ingredients may bemetered by means of the same metering device.

Preferably, the metering device 112 is a loss-in-weight gravimetricfeeder.

Generally, the rubber base materials, which are usually provided bymanufacturers in bales, are comminuted in irregular particles (crumbs)of small size (about 3-50 mm as average dimensions), e.g. by means ofblades, and then supplemented with an antisticking agent (e.g. chalk,silica, or other powders) to avoid reagglomeration.

Furthermore, gravimetrically controlled feeding pumps 113 are alsoprovided to introduce into the extruder 110 plasticizing oils andpossibly other liquid ingredients, such as silica coupling agents (e.g.silanes), adhesion promoters (e.g. cobalt salts), liquid resins (e.g.phenolic resins) and anti-reversion agents (e.g. silanes), which aregenerally added to the rubber base.

FIG. 1 shows also a flow D exiting from the extruder 110 which isgenerally provided with a degassing unit schematically indicated byreference sign 114.

Preferably, the extruder 110 is a co-rotating twin-screw extruder.

With reference to FIG. 1, the elastomeric composition is discharged fromthe extruder 110 by passing it through an extruder die 117 so that theelastomeric composition is obtained in the form of a continuouselastomeric ribbon E.

FIG. 2 shows a first embodiment of a continuous production plant 200according to the present invention, said plant 200 comprising theextruder 110 as described with reference to FIG. 1.

According to said embodiment, the elastomeric composition is filtered toeliminate any possible aggregate, metal particles or other impurities.To that purpose, a filtering body 212 (e.g. a screen filter) is placeddownstream of the extruder screw (not shown). During said filteringphase of the elastomeric composition particular care should be taken toavoid temperature raising which could cause scorching of the elastomericcomposition.

In order to impart to the extruded material a pressure sufficient topass said filtering body 212, preferably the extruder 110 is providedwith a gear pump 211. Preferably, said gear pump 211 is placed upstreamof the filtering body 212.

Preferably, said extruder 110 is a twin-screw extruder. Preferably, thescrews of the extruder 110 are co-rotating. Preferably, said co-rotatingintermeshing twin-screw extruder has a L/D ratio of 48.

According to said embodiment the continuous production plant 200 of thepresent invention further comprises a static mixer 210 which ispositioned at the discharge opening of the extruder 110. According tothe present invention, the static mixer 210 carries out homogenizing andmixing actions in order to confer to the elastomeric composition adesired consistency of the physical-chemical properties thereof. Theelastomeric composition is discharged from the static mixer 210 in theform of a continuous elastomeric ribbon F.

The static mixer which can be used in the process according to thepresent invention is generally a blending device, which is known per sein the art, containing no moving parts, in which the blending action isobtained by forcing the elastomeric composition to be blended to passthrough stationary blending elements. By diverting the direction of theflow or constraining this flow to pass through preferred channels, saidblending elements carry out numerous subdivisions and recombinations ofthe flow, thus making it possible to obtain the desired uniformity ofproperties within the elastomeric composition leaving the mixer. Thestatic mixer is preferably a device which is specially designed forblending highly viscous fluids and commonly used in processes ofinjection-moulding of plastics, for example a static mixer as disclosedin patent U.S. Pat. No. 5,564,827. In general, this type of mixercomprises static blending elements in a single piece, that is to saywithout welds or joints, so as to avoid as far as is possible anydeformations and/or ruptures inside the mixer, even when the material tobe blended is highly viscous and thus requires high extrusion pressures.

FIG. 3 shows a second embodiment of a continuous production plant 300according to the present invention, said plant 300 comprising theextruder 110 as described with reference to FIG. 1.

Preferably, the elastomeric ribbon E exiting from the extruder 110 iscooled down at a temperature not higher than 110° C. thanks to the airat ambient temperature surrounding said elastomeric ribbon during theconveying thereof to the successive operating units, by means of anysuitable device (e.g., a conveyor belt).

According to said embodiment the continuous production plant 300 of thepresent invention further comprises a static mixer 210 which ispositioned downstream of the extruder 110. The static mixer 210 is fedwith the elastomeric ribbon E by means of a feeding and pumping device310 and a gear pump 320 respectively. In order to impart to saidelastomeric composition E a pressure sufficient to pass through thestatic mixer 210, said elastomeric composition is fed to the feeding andpumping device 310 which, in turn, feeds the gear-pump 320 placeddownstream of said feeding and pumping device 310.

Preferably, said feeding and pumping device 310 is a single-screwextruder which is particularly preferred for feeding the gear-pump 320since a single-screw extruder does not cause the elastomeric compositionto remarkably increase the temperature thereof.

Finally, the elastomeric composition is discharged from the static mixer210 in the form of a continuous elastomeric ribbon F.

FIG. 4 shows a further embodiment of a continuous production plant 400of the present invention according to which the elastomeric ribbon Eexiting from the extruder 110 is conveyed, by means of any suitabledevice (e.g., a conveyor belt), to a grinding device 410 that transformsthe elastomeric ribbon E into an elastomeric subdivided product G.

Preferably, said grinding device 410 is a grinding mill or a granulator.

According to said further embodiment, the elastomeric subdivided productG is successively fed to the single-screw extruder 310 as disclosedabove with reference to the continuous production plant 300 of FIG. 3.

FIG. 5 shows a further embodiment of a continuous production plant 500of the present invention according to which the step of obtaining anelastomeric composition in the subdivided form is carried out directlyat the discharging opening of the extruder 110 so that the grindingdevice 410 of FIG. 4 can be avoided.

For example, according to said further embodiment the elastomericcomposition can be granulated at the end of the extrusion step byproviding the extrusion head with a perforated die plate 510 throughwhich the elastomeric composition is caused to pass.

The die plate 510 is generally equipped with cutting means (not shown inFIG. 5) so that the elastomeric composition can be obtained in thegranular form.

Analogously to the production plant 400 shown in FIG. 4, the elastomericcomposition in the subdivided form G is successively fed to thesingle-screw extruder 310, as mentioned above.

According to a further embodiment of the present invention, the minoringredients or part thereof (preferably the temperature sensitive minoringredients) re added to the resulting elastomeric composition ischargedfrom said at least one extruder.

According to an embodiment of the present invention, the extruder 110 isfed with rubber base materials, reinforcing fillers and minoringredients which are not temperature sensitive (such as crosslinkingagents, crosslinking accelerators, crosslinking retardants andcrosslinking activators) and, therefore, do not degrade and/or causescorching at the operating conditions and/or do not interfere with thecompounding process.

Alternatively, a predetermined amount of said temperature sensitiveminor ingredients is added to said resulting elastomeric compositionwhile the remaining part thereof is introduced into the extruderdirectly.

FIG. 6 shows an embodiment of a continuous production plant 600 of thepresent invention according to which the minor ingredients, or at leastpart of them, are added as masterbatches to the resulting elastomericcomposition discharged in the form of the elastomeric ribbon E from theextruder 110. In FIG. 6 two masterbatches H, I of two minor ingredientsare shown as a non-limitative example of the present invention.

Preferably, said masterbatches are obtained by mixing and dispersinginto an additional extruder (not shown) at least a predetermined amountof the resulting elastomeric composition discharged from the extruder110 and at least one minor ingredient.

According to an embodiment of the invention, each masterbatch includesone minor ingredient. Preferably, said minor ingredient is a temperaturesensitive minor ingredient.

According to a further embodiment, each masterbatch includes a mixtureof at least two minor ingredients.

In a preferred embodiment, the continuous production plant 600 furthercomprises the devices which are necessary for producing saidmasterbatches in situ. lternatively, said masterbatches are producedapart from the continuous productIon plant 600.

As shown in FIG. 6, after being metered (e.g. by means of any suitablemetering device such as a loss-in-weight gravimetric feeder), themasterbatches H, I are introduced into the feed hopper of thesingle-screw extruder 310 together with the elastomeric ribbon Edischarged from the extruder 110 and the process is successively carriedout as described above with reference to FIGS. 3 to 5.

According to a further embodiment of the present invention, thecontinuous production plant further comprises a stirring device.

In details, FIG. 7 shows an embodiment of a continuous production plant700 of the present invention according to which an amount of thesubdivided product G exiting from the grinding device 410 is accumulatedand stirred within a stirring device 710.

Preferably, the stirring device 710 is a rotating drum.

Preferably, the stirring step is carried out by continuously rotatingthe accumulated amount (e.g. by rotating the drum) so that subdividedproducts coming out from the grinding device 410 at different times areblended together.

The residence time of an elementary portion of the subdivided product(e.g. a granule) within the stirring device 710 depends on a pluralityof parameters such as: a) volume of the stirring device; b) rate flow ofthe subdivided product G; c) speed of rotation of the drum, in case thestirring device is a rotating drum; d) filling degree of the stirringdevice.

For example, in the case the stirring device is a rotating drum, theflow rate of the subdivided product is comprised from about 50 kg/h toabout 5,000 kg/h, the filling degree is of about 0.5, the drum volume iscomprised from about 1 m³ to about 5 m³, and the speed of rotation iscomprised from about 5 rpm to about 15 rpm (e.g. 6 rpm), the residencetime of the subdivided product within the rotating drum is preferably inthe range from 5 min to 15 min.

As shown in FIG. 7, at the end of the stirring step the stirredsubdivided product L is discharged from the stirring device 710 and fedto the single-screw extruder 310. Thus the process is successivelycarried out as described above with reference to FIGS. 3 to 6.

According to a further embodiment of the present invention, FIG. 8 showsa continuous production plant 800 wherein the step of obtaining anelastomeric composition in the subdivided form G is carried out directlyat the discharging opening of the extruder 110 as described above withreference to FIG. 5.

According to a further embodiment, masterbatches of the minoringredients are added to the resulting elastomeric composition (which isdischarged from the extruder 110) inside of the stirring device 710.

In details, FIG. 9 shows a continuous production plant 900 according towhich two masterbatches H′, I′ of two minor ingredients in thesubdivided form and the resulting elastomeric composition in thesubdivided form G exiting from the extruder 110 are fed to the stirringdevice 710.

FIG. 10 shows a continuous production plant 950 of the present inventionaccording to which the minor ingredients, or at least part of them, areadded to the stirred elastomeric composition inside of the single-screwextruder.

According to said embodiment the elastomeric composition in thesubdivided form G is stirred into the stirring device 710 andsuccessively added to the minor ingredients H, I. Preferably, said minoringredients H, I are in the form of masterbatches as described above.Preferably, said masterbatches are reduced in the subdivided form.Alternatively, said masterbatches are introduced (injected) into thesingle-screw extruder 310 in the form of a ribbon.

According to a preferred embodiment of the present invention, one ormore recipe ingredients are fed to the respective metering devices inthe subdivided form.

Preferably the minor ingredients are fed in the subdivided form.

According to a further embodiment of the present invention, one or morerecipe ingredients are conveyed to respective metering devices by meansof a pneumatic conveying line.

When a pneumatic conveying line is used, preferably at least one minoringredient is provided to the production plant in a subdividedfree-flowing form which is particularly suitable for the pneumaticconveying thereof.

Preferably said free-flowing properties as well as high dimensionalregularity and stability are obtained by dispersing said at least oneminor ingredient in a thermoplastic binding agent.

Moreover, the thermoplastic binding agent readily melts when introducedinto the extruder, thus acting as a processing aid and remarkablyimproving the dispersion of said at least one minor ingredient into therubber base, without causing any significant changes in the propertiesof the final elastomeric composition.

Minor ingredients which can be metered and fed to the extruder in thesubdivided form may be selected, for instance, from:

-   -   (a1) crosslinking agents, such as:        -   sulfur (usually in a soluble crystalline form or in a            insoluble polymeric form, optionally dispersed in an oily            phase); sulfur donors (e.g. alkylthiuram disulfides);            organic peroxides;    -   (a2) crosslinking accelerators, such as:        -   thiazoles, sulfenamides, guanidines, thiurams,            dithiocarbamates, amines, xanthogenates;    -   (a3) synthetic resins, such as alpha-methylstyrene resins,        cumarone resins;    -   (a4) crosslinking activators, such as zinc compounds (e.g. ZnO,        ZnCO₃, fatty acid zinc salts);    -   (a5) crosslinking retardants, such as carboxylic acids,        phthalimide derivatives, diphenylamine derivatives;    -   (a6) adhesion promoters, such as hexamethylentetramine (HMT),        resorcinol;    -   (a7) protective agents, such as aromatic diamines (e.g.        N-(1,3-dimethylbutyl)-N′-p-phenylendiamine (6PPD)),        dihydrochinoline derivatives, imidazole derivatives;    -   (a8) coupling agents, such as coupling agents for silica,        particularly sulfur-containing hydrolyzable silanes (e.g.        3,3′-bis(triethoxy-silylpropyl)tetrasulfide (TESPT));    -   (a9) condensation catalysts, such as metal carboxylates (e.g.        dibutyltindilaurate (DBTL)).

The above list is given only to illustrate some examples of the mostcommon minor ingredients used in rubber mixtures, particularly in rubbermixtures for tyres, and shall not be intended as limitative of the scopeof the present invention.

The process according to the present invention may be employed toproduce rubber mixture of any kind of elastomers, particularly ofelastomers used in the tyre industry. Generally, the elastomeric basemay be selected from: diene elastomeric polymers and mono-olefinelastomeric polymers, or mixtures thereof.

Diene elastomeric polymers are generally of natural origin, or may beobtained by polymerization, in solution or in emulsion, of at least oneconjugated diolefin, optionally with at least one monovinylarene in anamount not exceeding 50% by weight. Examples of diene elastomericpolymers are: cis-1,4-polyisoprene (either natural or synthetic,preferably natural rubber), 3,4-polyisoprene, poly-1,3-butadiene (inparticular, high vinyl poly-1,3-butadiene having a content of1,2-polymerized units of from 15% to 85% by weight), polychloroprene,optionally halogenated isoprene/isobutene copolymers,1,3-butadiene/acrylonitrile copolymers, 1,3-butadiene/styrenecopolymers, 1,3-butadiene/isoprene copolymers, isoprene/styrenecopolymers, isoprene/1,3-butadiene/styrene terpolymers; or mixturesthereof.

As to mono-olefin elastomeric polymers, they may be selected from:copolymers of ethylene with at least one alpha-olefin having from 3 to12 carbon atoms, and optionally with a diene having from 4 to 12 carbonatoms; polyisobutene; copolymers of isobutene with at least one diene.Particularly preferred are: ethylene/propylene copolymers (EPR);ethylene/propylene/diene terpolymers (EPDM); polyisobutene; butylrubbers; halobutyl rubbers; or mixtures thereof.

The rubber mixture further comprises at least one reinforcing filler,such as: carbon black, silica, alumina, aluminosilicates, calciumcarbonate, kaolin, titanium dioxide, or mixtures thereof. Particularlypreferred are carbon black and silica, or mixtures thereof. The amountof the reinforcing filler may be generally of from 0.1 to 120 phr,preferably from 20 to 90 phr (phr=parts by weight per 100 parts byweight of total elastomeric base).

To improve processability, at least one plasticizing agent is preferablyadded to the rubber mixtures. It is generally selected from mineraloils, vegetable oils, synthetic oils and the like, or mixtures thereof,for instance: aromatic oil, naphthene oil, phthalates, soybean oil, ormixtures thereof. The amount of the plasticizing agent may generallyrange from 2 to 100 phr, preferably from 5 to 50 phr.

The present invention is now further illustrated by the followingworking examples.

EXAMPLE 1 (INVENTION)

An elastomeric composition was produced according to the schematicproduction process of FIG. 4.

Said elastomeric composition was prepared by using natural rubber (NR)and butadiene rubber (BR) as elastomeric base, and carbon black asreinforcing filler.

The recipe of the elastomeric composition is reported in Table 1hereinbelow. TABLE 1 Ingredients phr NR (STR 20) 50 BR (polybutadieneBuna ® Cis-132 - Bayer) 50 Carbon Black N660 50 Minor Zinc Oxide 3Ingredients Wax 2 Stearic Acid 2 N-tertbutyl-mercaptobenzothiazyl 0.8sulphenamide (TBBS) Insoluble sulfur (S_(n)) 1.8 N-cyclohexylthiophtaloimide (PVI) 0.3 Antioxidant (6PPD) 2.5 Total 162.4

The term “phr” indicates the parts by weight per 100 parts by weight oftotal rubber.

The natural rubber and the butadiene rubber were obtained in the form ofgranules, having an average particle size of about 1 cm, by means of twomills provided with rotating blades.

In order to prevent reagglomeration, the obtained granules of the tworubbers were dusted with silica.

Successively, a mechanical blending of the granules of the two rubberswas carried out and the blended granules of the two different rubberswere fed to a first feeding hopper (the main hopper) of a co-rotatingintermeshing twin-screw extruder having a cylinder diameter of 58 mm anda L/D ratio of 48.

The feeding of said blended granules to the twin-screw extruder wascarried out by means of a gravimetric feeder.

The minor ingredients in the form of powders were introduced atdifferent zones of the twin-screw extruder.

About 50% by weight of the reinforcing filler, i.e. of the carbon black,was fed together with the granulated rubbers to the first feeding hopperof the twin-screw extruder by means of a dedicated gravimetric feeder.

The remaining part of carbon black as well as zinc oxide, wax andstearic acid were fed to a second feeding hopper of the twin-screwextruder by means of a different dedicated gravimetric feeder, i.e. agravimetric feeder for each ingredient.

Insoluble sulphur, N-cyclohexyl thiophtaloimide (PVI) and N-tertbutylmercaptobenzothiazyl sulphenamide (TBBS), i.e. the curatives, were fedto a further feeding hopper of the twin-screw extruder by means ofdedicated gravimetric feeders.

Antioxidant 6PPD was injected in the molten state by means of agravimetrically controlled feeding pump.

In order to determine the weight errors introduced by the feedinggravimetric system into the production process, each gravimetric feederwas provided with an on-line electronic control device which measuredand displayed the instant flow of the recipe ingredient. If necessary,said control was able to correct the instant flow by acting on thefeeding mechanism of the gravimetric feeder.

The extruded elastomeric composition was in the form of a continuousribbon having width of about 10 cm and thickness of about 2 cm.

Said ribbon was fed to a mill provided with rotating blades so as topelletize said ribbon in order to obtain elastomeric granules havingaverage particle size of about 1 cm.

100 kg of elastomeric composition in the granular form was produced anddusted with silica in order to prevent reagglomeration.

Successively, said granules amount was fed to a single-screw extruderhaving a cylinder diameter of 50 mm and a L/D ratio of 12.

The single-screw extruder performed the step of feeding the elastomericcomposition to a static mixer (Sulzer SMK-X DN 30 produced by SulzerChemtech Ltd.) for homogenizing the extrudate exiting from saidsingle-screw extruder.

The elastomeric composition exiting from the static mixer was at atemperature of about 130° C. and was in the form of a rod having adiameter of about 3 cm.

Eight samples were obtained from said rod (each sample having acylindrical form with length of about 25 mm and diameter of about 14 mm)and submitted to a curing step for 10 minutes at 170° C.

Successively said samples were tested to evaluate the followingproperties:

-   -   Mooney viscosity ML(1+4) at 100° C. according to Standard ISO        289/1;    -   mechanical properties (100% Modulus, 300% Modulus, stress at        break, elongation at break) according to ISO Standard 37;    -   dynamic elastic properties, and

hardness in IRHD degrees at 23° C. and 100° C. according to ISO Standard48.

In Table 2 are reported the arithmetical mean values for each propertyof the tested samples.

The dynamic elastic properties were measured with a dynamic Instrondevice in the compression mode according to the following method. Eachsample, compression-preloaded up to a lot longitudinal deformation withrespect to the initial length and kept at the prefixed temperature (70°C. or 23° C.) for the whole duration of the test, was submitted to adynamic sinusoidal strain having an amplitude of ±3.33% with respect tothe length under pre-load, with a 100 Hz frequency. The dynamic elasticproperties were expressed in terms of dynamic elastic modulus (E′) andtandelta (loss factor) values. The tandelta value was calculated as aratio between the viscous modulus (E″) and the elastic modulus (E′),both of them being determined with the above dynamic measurements.

With reference to the samples mentioned above, for each of the testedproperty the Applicant calculated the root-mean-square deviation (σ) andthe scattering coefficient (V) in order to quantify the scattering ofthe measured values from the average value. TABLE 2 Root-mean-Scattering square coefficient Average deviation V Test value σ (%)Viscosity 45.40 0.634 1.41 (ML 1 + 4 100° C.) 100% Modulus 1.34 0.0413.06 (MPa) 300% Modulus 6.25 0.289 4.62 (MPa) Stress at break 15.310.711 4.64 (MPa) Elongation at break 590.50 14.281 2.42 (%) E′ (23° C.)5.059 0.072 1.42 (MPa) E′ (70° C.) 3.968 0.091 2.29 (MPa) Tan delta (23°C.) 0.164 0.002 1.45 Tan delta (70° C.) 1.137 0.004 0.36 IRHD Hardness53.20 0.532 1.00 (23° C.) IRHD Hardness 51.60 0.620 1.20 (100° C.)wherein the scattering coefficient V is calculated as follows:$\begin{matrix}{{V = \frac{\sigma}{\overset{\_}{x}}}{or}} & (1) \\{{V\quad\%} = {100*\frac{\sigma}{\overset{\_}{x}}}} & (2)\end{matrix}$wherein:

-   -   {overscore (x)} is the arithmetical mean of the measured values        of the property x for all the samples, i.e.: $\begin{matrix}        {\overset{\_}{x} = {\frac{1}{N}{\sum\limits_{i = 1}^{N}x_{i}}}} & (3)        \end{matrix}$    -   N is the total number of samples which have been considered; and    -   σ is the root-mean-square deviation that is calculated as        follows: $\begin{matrix}        {\sigma = \sqrt{\frac{\sum\limits_{i = 1}^{N}\left( {x_{i} - \overset{\_}{x}} \right)^{2}}{N - 1}}} & (5)        \end{matrix}$

Since the scattering coefficient V is directly proportional to theroot-mean-square deviation σ, the greater is the value of V, the greateris the value of σ, i.e. the greater is the amplitude of the Gaussiancurve centered in correspondence of the average value {overscore (x)}.Of course, the greater is the value of V, the greater is theinconsistency of the measured physical-chemical properties from sampleto sample.

EXAMPLE 2 (INVENTION)

The elastomeric composition of the Example 1 was processed in acontinuous production plant of the type shown in FIG. 7.

Said elastomeric composition was submitted to the same productionprocedure and the same operating conditions of Example 1 except for thefact that the elastomeric composition in the granular form exiting fromthe mill was fed to a rotating drum.

100 kg of elastomeric composition in the granular form was produced anddusted with silica in order to prevent reagglomeration.

Successively, said granules amount was fed to said rotating drum havinga capacity of 1,500 litres and stirred for 10 minutes at a rotationspeed of about 25 rpm so as to homogenize the pelletized extrudate.

At the end of the stirring step, the rotating drum. was stopped and thedischarged granules were fed to the single-screw extruder associated tothe static mixer, as described in Example 1.

Analogously to Example 1, the resulting elastomeric composition exitingfrom the static mixer was in the form of a rod of a diameter of about 3cm, at a temperature of about 130° C.

Eight samples were obtained from said rod (each sample having acylindrical form with length of about 25 mm and diameter of about 14 mm)and submitted to a curing step for 10 minutes at 170° C.

Successively, said samples were tested to evaluate the abovementionedproperties (as described in Example 1), the results of which arereported in Table 3.

In Table 3 are reported the arithmetical mean values for each propertyof the tested samples. TABLE 3 Root-mean- Scattering square coefficientAverage deviation V Test value σ (%) Viscosity 46.00 0.359 0.78 (ML 1 +4 100° C.) 100% Modulus 1.55 0.017 1.10 (MPa) 300% Modulus 7.24 0.0191.55 (MPa) Stress at break 14.81 0.376 2.54 (MPa) Elongation at break538.20 13.616 2.53 (%) E′ (23° C.) 4.89 0.129 2.64 (MPa) E′ (70° C.)4.02 0.088 2.19 (MPa) Tan delta (23° C.) 0.148 0.003 1.35 Tan delta (70°C.) 0.113 0.002 1.77 IRHD Hardness 57.30 0.201 0.35 (23° C.) IRHDHardness 53.60 0.247 0.46 (100° C.)

EXAMPLE 3 (INVENTION)

An elastomeric composition was produced according to the schematicproduction process of FIG. 9.

Said elastomeric composition was prepared by using natural rubber (NR)and butadiene rubber (BR) as elastomeric base, and carbon black asreinforcing filler.

The recipe of the elastomeric composition is reported in Table 4hereinbelow. TABLE 4 Ingredients phr NR (STR 20) 50 BR (polybutadieneBuna ® Cis-132 - Bayer) 50 Carbon Black N660 50 Minor Zinc Oxide 3Ingredients Wax 2 Stearic Acid 2 Antioxidant (6PPD) 2.9 Total 159.5

As described in Example 1, the natural rubber and the butadiene rubber,obtained in the form of granules, after blending were fed to a firstfeeding hopper (the main hopper) of a co-rotating intermeshingtwin-screw extruder having a cylinder diameter of 58 mm and a L/D ratioof 48.

The minor ingredients indicated in Table 4 were introduced in the formof powders at different zones of the twin-screw extruder.

About 50% by weight of the reinforcing filler, i.e. of the carbon black,was fed together with the granulated rubbers to the first feeding hopperwhile the remaining part of carbon black as well as zinc oxide, wax andstearic acid were fed to a second feeding hopper of the twin-screwextruder.

Antioxidant 6PPD was injected in the molten state by means of agravimetrically controlled feeding pump.

Insoluble sulphur, N-cyclohexyl thiophtaloimide (PVI) and N-tertbutylmercaptobenzothiazyl sulphenamide (TBBS), i.e. the curatives, were notprocessed inside of the twin-screw extruder and were added to theresulting elastomeric composition, exiting from the twin-screw extruder,by means of two masterbatches having the compositions reported in Tables5 and 6. TABLE 5 Masterbatch 1 phr Elastomeric composition from thetwin-screw 100 extruder Minor Insoluble sulfur (S_(n)) 11.50 IngredientsN-cyclohexyl thiophtaloimide (PVI) 1.92 Total 113.42

TABLE 6 Masterbatch 2 phr Elastomeric composition from the twin-screw100 extruder Minor N-tertbutyl-mercaptobenzothiazyl 5.74 Ingredientsulphenamide (TBBS) Total 105.74

Masterbatches 1 and 2 were prepared apart from the production plantshown in FIG. 9 by means of a further twin-screw extruder fed with thepredetermined amount of elastomeric composition (exiting from theextruder) and the temperature sensitive minor ingredients according tothe recipes reported in Tables 5 and 6 respectively.

Successively, masterbatches 1 and 2 were pelletized by using a cuttingdevice so as to obtain granules having average particle size of about 5mm.

The resulting elastomeric composition, exiting from the twin-screwextruder, was pelletized in order to obtain elastomeric granules havingaverage particle size of about 1 cm. According to the embodimentdescribed in FIG. 9, the elastomeric composition was pelletized directlyat the discharging opening of the extruder by providing the extrusionhead with a perforated die plate through which the elastomericcomposition was caused to pass.

80 kg of the resulting elastomeric composition exiting from thetwin-screw extruder, 10.93 kg of masterbatch 1 and 9.07 kg ofmasterbatch 2 (100 kg in total) were fed to a rotating drum having acapacity of 1,500 litres and stirred for 10 minutes at a rotation speedof about 25 rpm so as to homogenize the pelletized extrudate.

At the end of the stirring step, the rotating drum was stopped and thedischarged granules were fed to the single-screw extruder associated tothe static mixer, as described in Example 1.

Analogously to Example 1, the resulting elastomeric composition (exitingfrom the static mixer) was in the form of a rod of a diameter of about 3cm, at a temperature of about 133° C.

Five samples were obtained from said rod (each sample having acylindrical form with length of about 25 mm and diameter of about 14 mm)and submitted to a curing step for 10 minutes at 170° C.

Successively, said samples were tested to evaluate the abovementionedproperties, the results of which are reported in Table 7.

In Table 7 are reported the arithmetical mean values for each propertyof the tested samples. TABLE 7 Root-mean- Scattering square coefficientAverage deviation V Test value σ (%) Viscosity 60.76 0.666 1.10 (ML 1 +4 100° C.) 100% Modulus 1.59 0.022 1.38 (MPa) 300% Modulus 6.87 0.1341.95 (MPa) Stress at break 14.64 0.625 4.27 (MPa) Elongation at break560.60 19.835 3.46 (%) E′ (23° C.) 4.918 0.055 1.12 (MPa) E′ (70° C.)4.061 0.028 0.69 (MPa) Tan delta (23° C.) 0.162 0.003 1.85 Tan delta(70° C.) 0.132 0.001 0.76 IRHD Hardness 57.78 0.337 0.65 (23° C.) IRHDHardness 52.04 0.757 1.45 (100° C.)

EXAMPLE 4 (COMPARATIVE)

The elastomeric composition of the Example 1 was metered and fed to aco-rotating intermeshing twin-screw extruder according to the continuousproduction plant shown in FIG. 1.

Said elastomeric composition was prepared by using natural rubber (NR)and butadiene rubber (BR) as elastomeric base, and carbon black asreinforcing filler.

The natural rubber and the butadiene rubber were obtained in the form ofgranules, having an average particle size of about 1 cm, by means of twomills provided with rotating blades.

In order to prevent reagglomeration, the obtained granules of the tworubbers were dusted with silica.

Successively, a mechanical blending of the granules of the two rubberswas carried out and the blended granules of the two different rubberswere fed to a first feeding hopper (the main hopper) of a co-rotatingintermeshing twin-screw extruder having a cylinder diameter of 58 mm anda L/D ratio of 48.

The feeding of said blended granules to the twin-screw extruder wascarried out by means of a gravimetric feeder.

The minor ingredients in the form of powders were introduced atdifferent zones of the twin-screw extruder.

About 50% by weight of the reinforcing filler, i.e. of the carbon black,was fed together with the granulated rubbers to the first feeding hopperof the twin-screw extruder by means of a dedicated gravimetric feeder.

The remaining part of carbon black as well as zinc oxide, wax andstearic acid were fed to a second feeding hopper of the twin-screwextruder by means of a different dedicated gravimetric feeder, i.e. agravimetric feeder for each ingredient.

Insoluble sulphur, N-cyclohexyl thiophtaloimide (PVI) and N-tertbutylmercaptobenzothiazyl sulphenamide (TBBS), i.e. the curatives, were fedto a further feeding hopper of the twin-screw extruder by means ofdedicated gravimetric feeders.

Antioxidant 6PPD was injected in the molten state by means of agravimetrically controlled feeding pump.

The extruded elastomeric composition was in the form of a continuousribbon having width of about 10 cm and thickness of about 2 cm. Thetemperature of the extrudate was of about 126° C.

From said ribbon ten samples were obtained, submitted to curing for 10min at 170° C. and tested to evaluate the physical-chemical propertiesthereof.

The results are reported in Table 8. TABLE 8 Root-mean- Scatteringsquare coefficient Average deviation V Test value σ (%) Viscosity 40.9321.533 3.75 (ML 1 + 4 100° C.) 100% Modulus 1.529 0.149 9.74 (MPa) 300%Modulus 7.113 0.652 9.17 (MPa) Stress at break 14.772 0.661 4.47 (MPa)Elongation at break 546.190 36.070 6.60 (%) E′ (23° C.) 4.99 0.123 2.46(MPa) E′ (70° C.) 3.96 0.128 3.23 (MPa) Tan delta (23° C.) 0.161 0.0042.48 Tan delta (70° C.) 1.130 0.009 6.92 IRHD Hardness 56.070 1.818 3.24(23° C.) IRHD Hardness 52.260 1.891 3.62 (100° C.)

By comparing the values reported in Tables 2, 3, 7 and 8, it can bepointed out that the scattering coefficients V relative to the measuredphysical-chemical properties of the elastomeric samples obtained withthe production processes of the present invention are remarkably lowerthan the corresponding scattering coefficients V of the elastomericsamples obtained with a traditional production process.

As mentioned above, the fact that the scattering coefficients V can benotably reduced is particularly advantageous since very low scatteringcoefficients mean that the physical-chemical properties of theelastomeric composition obtained from the production process accordingto the present invention are substantially consistent during the wholeduration of the production campaign.

This means that elastomeric manufactured products obtained from the samerecipe at different moments of the production process are expected toshow uniformity of properties as well as high quality consistency sothat substantially the same behaviour can be ensured from product toproduct belonging to the same production campaign.

Furthermore, if compared to prior art continuous processes provided withtwo twin-screw extruders, the continuous production process according tothe present invention gives good results in terms of scattering of thephysical-chemical properties of the resulting elastomeric compositionand is advantageously less expensive and less complex to be carried out.

1-46. (canceled)
 47. A process for continuously producing an elastomericcomposition, comprising: metering and feeding at least one elastomer andat least one filler into at least one extruder; mixing and dispersingthe at least one filler into the at least one elastomer using the atleast one extruder; and passing the elastomeric composition that resultsthrough at least one static mixer.
 48. The process of claim 47, furthercomprising: discharging the resulting elastomeric composition from theat least one extruder; wherein the discharging is carried out beforepassing the resulting elastomeric composition.
 49. The process of claim48, further comprising: cooling the resulting elastomeric compositiondischarged from the at least one extruder.
 50. The process of claim 49,wherein the resulting elastomeric composition is cooled down at atemperature less than or equal to 110° C.
 51. The process of claim 49,wherein the resulting elastomeric composition is cooled down at atemperature greater than or equal to 20° C. and less than or equal to90° C.
 52. The process of claim 47, further comprising: metering andfeeding at least one minor ingredient into the at least one extruder.53. The process of claim 52, further comprising: mixing and dispersingthe at least one minor ingredient into the at least one elastomer usingthe at least one extruder.
 54. The process of claim 52, wherein the atleast one minor ingredient is selected from: crosslinking agents,crosslinking accelerators, resins, crosslinking activators, crosslinkingretardants, adhesion promoters, protective agents, coupling agents, andcondensation catalysts.
 55. The process of claim 52, wherein the atleast one minor ingredient does not include a temperature-sensitiveminor ingredient.
 56. The process of claim 52, wherein the at least oneminor ingredient includes at least one temperature-sensitive minoringredient.
 57. The process of claim 52, wherein the at least one minoringredient is in a form of a subdivided product.
 58. The process ofclaim 52, wherein the at least one minor ingredient is in a form of apowder.
 59. The process of claim 52, wherein the at least one minoringredient is in a form of a masterbatch.
 60. The process of claim 59,wherein the masterbatch is obtained in a form of a subdivided product.61. The process of claim 60, further comprising: accumulating an amountof the subdivided product; and stirring the accumulated amount.
 62. Theprocess of claim 59, wherein the masterbatch comprises: the at least oneminor ingredient; and the resulting elastomeric composition.
 63. Theprocess of claim 62, wherein the masterbatch is obtained in a form of asubdivided product.
 64. The process of claim 63, further comprising:accumulating an amount of the subdivided product; and stirring theaccumulated amount.
 65. The process of claim 48, further comprising:adding at least one minor ingredient to the resulting elastomericcomposition discharged from the at least one extruder.
 66. The processof claim 65, wherein the at least one minor ingredient is selected from:crosslinking agents, crosslinking accelerators, resins, crosslinkingactivators, crosslinking retardants, adhesion promoters, protectiveagents, coupling agents, and condensation catalysts.
 67. The process ofclaim 65, wherein the at least one minor ingredient includes at leastone temperature-sensitive minor ingredient.
 68. The process of claim 65,wherein the at least one minor ingredient is in a form of a subdividedproduct.
 69. The process of claim 65, wherein the at least one minoringredient is in a form of a powder.
 70. The process of claim 65,wherein the at least one minor ingredient is in a form of a masterbatch.71. The process of claim 70, wherein the masterbatch is obtained in aform of a subdivided product.
 72. The process of claim 71, furthercomprising: accumulating an amount of the subdivided product; andstirring the accumulated amount.
 73. The process of claim 70, whereinthe masterbatch comprises: the at least one minor ingredient; and theresulting elastomeric composition discharged from the at least oneextruder.
 74. The process of claim 73, wherein the masterbatch isobtained in a form of a subdivided product.
 75. The process of claim 74,further comprising: accumulating an amount of the subdivided product;and stirring the accumulated amount.
 76. The process of claim 48,further comprising: obtaining a subdivided product from the resultingelastomeric composition discharged from the at least one extruder. 77.The process of claim 76, wherein obtaining the subdivided product iscarried out at a discharge opening of the at least one extruder.
 78. Theprocess of claim 48, further comprising: cooling the resultingelastomeric composition discharged from the at least one extruder; andobtaining a subdivided product from the resulting elastomericcomposition discharged from the at least one extruder; wherein obtainingthe subdivided product is carried out after cooling the resultingelastomeric composition.
 79. The process of claim 76, furthercomprising: accumulating an amount of the subdivided product; andstirring the accumulated amount.
 80. The process of claim 48, furthercomprising: adding at least one minor ingredient to the resultingelastomeric composition discharged from the at least one extruder;obtaining a subdivided product from the resulting elastomericcomposition discharged from the at least one extruder; accumulating anamount of the subdivided product; and stirring the accumulated amount;wherein adding the at least one minor ingredient is carried out beforeaccumulating an amount of the subdivided product and stirring theaccumulated amount.
 81. The process of claim 48, further comprising:adding at least one minor ingredient to the resulting elastomericcomposition discharged from the at least one extruder; obtaining asubdivided product from the resulting elastomeric composition dischargedfrom the at least one extruder; accumulating an amount of the subdividedproduct; and stirring the accumulated amount; wherein adding the atleast one minor ingredient is carried out after accumulating an amountof the subdivided product and stirring the accumulated amount.
 82. Theprocess of claim 47, further comprising: discharging the elastomericcomposition from the at least one static mixer.
 83. The process of claim82, wherein discharging the elastomeric composition is carried outcontinuously.
 84. The process of claim 82, wherein discharging theelastomeric composition is carried out batchwise.
 85. An apparatus forcontinuously producing an elastomeric composition, comprising: at leastone twin-screw extruder; at least one metering device; and at least onestatic mixer; wherein the at least one extruder comprises: a housing;and two screws rotatably mounted in the housing; wherein the housingcomprises: at least one feed opening; and a discharge opening; whereinthe at least one metering device meters and feeds at least one elastomerand at least one filler into the at least one extruder, and wherein theelastomeric composition discharged from the discharge opening passesthrough the at least one static mixer.
 86. The apparatus of claim 85,wherein the at least one metering device is a gravimetric feeder. 87.The apparatus of claim 85, wherein the at least one static mixer isdisposed at the discharge opening.
 88. The apparatus of claim 85,wherein the at least one static mixer is disposed downstream of the atleast one extruder.
 89. The apparatus of claim 85, further comprising:at least one further metering device to meter and feed at least oneminor ingredient into the at least one extruder.
 90. The apparatus ofclaim 89, wherein the at least one minor ingredient comprises at leastone temperature-sensitive minor ingredient.
 91. The apparatus of claim88, further comprising: at least one further metering device to meterand add at least one minor ingredient to the elastomeric compositiondischarged from the discharge opening.
 92. The apparatus of claim 91,wherein the at least one further metering device is a gravimetricfeeder.
 93. The apparatus of claim 91, wherein the at least one minoringredient comprises at least one temperature-sensitive minoringredient.
 94. The apparatus of claim 88, further comprising: at leastone cooling device upstream of the at least one static mixer.
 95. Theapparatus of claim 88, further comprising: at least one device forobtaining a subdivided product from the elastomeric compositiondischarged from the discharge opening.
 96. The apparatus of claim 95,wherein the at least one device for obtaining a subdivided product isdisposed at the discharge opening.
 97. The apparatus of claim 96,wherein the at least one device for obtaining a subdivided product is aperforated die plate equipped with cutting means.
 98. The apparatus ofclaim 95, wherein the at least one device for obtaining a subdividedproduct is a granulator or an open mill.
 99. The apparatus of claim 95,further comprising: at least one stirring device; wherein the at leastone stirring device mixes an accumulated amount of the subdividedproduct.
 100. The apparatus of claim 99, wherein the at least onestirring device is disposed upstream of the at least one static mixer.101. The apparatus of claim 99, wherein the at least one stirring deviceis a rotating drum.
 102. The apparatus of claim 87, further comprising:a feeding and pumping device disposed upstream of the at least onestatic mixer.
 103. The apparatus of claim 102, wherein the feeding andpumping device is a gear pump.
 104. The apparatus of claim 88, furthercomprising: a feeding and pumping device disposed at a feed opening ofthe at least one static mixer.
 105. The apparatus of claim 104, whereinthe feeding and pumping device comprises one or more of: a gear pump, asingle-screw extruder, and a reciprocating screw.
 106. The apparatus ofclaim 85, further comprising: at least one filtering body positionedupstream of the discharge opening.